A sputtering process, an MBE process, a pulsed laser deposition process, an MOCVD process, or another process is used to produce a thin-film of single-crystalline multi-element oxide, such as Bi4Ti3O12, containing bismuth as well known (see, for example, Patent Documents 1 to 6). Furthermore, the following process is used to produce a single crystal as well known: a flux process for growing a single crystal in a solution using a flux that is a compound which does not react with a target substance and raw materials and which can be readily separated therefrom (see Patent Document 7). A Bi2O3 flux is used to produce a bulk single crystal of Bi4Ti3O12 by such a flux process (see Non-patent Documents 1 and 2).
Fluxes are additives used to produce single crystals. The fluxes promote the growth of crystals and enable the synthesis of a thermodynamically unstable substance by reducing the synthesis temperature. Flux epitaxy is a process for fabricating a thin-film using a flux (see Non-patent Documents 3 and 4). It has been recently found that a high-quality bulk single-crystalline thin-film can be fabricated by the flux epitaxy.
The inventors have filed a patent application claiming invention for a method for producing a single-crystalline oxide thin-film by a three-phase epitaxial process (see Patent Document 8). In this method, a flux layer is formed by depositing a flux material on a wafer in advance such that a flux layer is formed on the wafer and a high-quality thin-film is deposited on the flux layer, the flux material being Ba—Cu—O. The flux material is known in the field of bulk single crystal production and provides an element of an NdBa2Cu3O7 single crystal.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 61-6124    Patent Document 2: Japanese Unexamined Patent Application Publication No. 63-171869 (Japanese Patent No. 2547203)    Patent Document 3: Japanese Unexamined Patent Application Publication No. 63-171870 (Japanese Patent No. 2547204)    Patent Document 4: Japanese Unexamined Patent Application Publication No. 05-246722 (Japanese Patent No. 3195827)    Patent Document 5: Japanese Unexamined Patent Application Publication No. 09-67197    Patent Document 6: Japanese Unexamined Patent Application Publication No. 10-158094 (Japanese Patent No. 2939530)    Patent Document 7: Japanese Unexamined Patent Application Publication No. 10-338599    Patent Document 8: Japanese Unexamined Patent Application Publication No. 2002-68893    Non-patent Document 1: Yoichiro Matsuda, Hiroshi Matsumoto, Akira Baba, Takashi Goto, and Toshio Hirai, Jpn. J. Appl. Phys., Vol. 31, (1992) 3108    Non-patent Document 2: Rintaro Aoyagi, Hiroaki Takeda, Soichiro Okamura, Tadashi Shiosaki, Jpn. J. Appl. Phys., Vol. 40, (2001) 5671    Non-patent Document 3: K. S. Yun, B. D. Choi, Y. Matsumoto, J. H. Song, N. Kanda, T. Itoh, M. kawasaki, T. Chikyowl and P. Ahmet, H. Koinuma, Appl. Phys. Lett. 80, 61-63 (2002)    Non-patent Document 4: Ryuta Takahashi et. al., “Dai 50 Kai Ouyoubutsurigaku Kankeirengou Kouenkai Kouenyokoushu”, p. 658, (March 2003)